What generally happens when a second colour is brushed over wet paint?

Correct answer: The colours blend softly

The governing concept is the wet-on-wet method, in which a new colour is applied while the first layer is still moist. Because water remains active in both areas, the pigments spread slightly into one another and create a soft transition rather than a sharp boundary. Thus option D is correct. A completely separate colour or a hard edge is more likely when the underlying paint has dried, while wet paint cannot make the paper dry immediately.